The invention relates to a nondestructive flaw detection method, especially an ultrasonic flaw detection method for detecting rail flaws, as well as the wheel transducer and flaw detection system for implementing the method.
In the technical fields in which it is necessary to ensure high safety and high reliability, such as industries of defense, aerospace and railway communications, nondestructive flaw detection methods are broadly used in detecting various flaws possibly present in key elements or units. In the field of railway communications, the nondestructive flaw detection system should have high detecting precision and high detecting rate, and, at present; a wheel-type system that can continuously detect rail flaws is generally adopted. U.S. Pat. No. 4,487,071 disclosed such a flaw detection system which includes, as shown in FIG. 1, wheel transducers 1, detecting supports 7, guiding wheels 8 for guiding the detecting supports and detecting support links 9 which fix the detection system on a flaw detection car 13. Each of the wheel transducers 1 comprises a tire 10 made of sound wave permeable thin rubber and filled with coupling fluid 6 for transmitting sound wave, as shown in FIGS. 2(a) and 2(b). The wheel transducer 1 further comprises probes 5 functioning as ultrasonic emuitter/receiver. When detecting flaws, the probes 5 continuously emit ultrasonic pulse beams 14, which pass through the coupling fluid 6 and the tire 10 into the rail 15 to be detected. If no flaw is present in the rail, the beams 14 arrive at the bottom surface of the rail and are reflected to the probes, resulting in a background wave. If there is a flaw in the rail, a flaw wave is obtained before the background wave (as shown in FIG. 6(a)). The probes 5 receive the reflected echo signal and deliver it to a processing unit 12, which outputs continuous detection results.
However, said flaw detection system has the following main disadvantages. Firstly, because the distance from the,probes to the rail is relatively long, and the sound wave""s propagation velocity in the coupling fluid is relatively small (approximately ⅕ of that in steel), the sound wave is delayed and when the detecting rate increases, the echo wave will progressively drop behind fori a certain distance and cannot be received correctly by the probes, which results in signal missing. Secondly, when the wheel transducer having thin-wall tire and internal coupling fluid rotates in high speed, the viscosity, tlie inertia of the internal coupling fluid and the weak elasticity of the external wall of the thin rubber tire lead to interfering force, and, as results, the wheel transducer cannot retain a planar coupling surface which is necessary for detecting operation. Accordingly, the emitting and reflecting of the ultrasonic sound wave are cumbered, or interfering reflecting surfaces occur, and the missing echo signals and interfering waves increase. Finally, in order to avoid vibrating of the wheel transducer, the detecting support must be yvery heavy (typically greater than 1 ton) and very solid. Accordingly, when the detecting support moves in high speed, the great inertia force makes the detecting support not so easy to be guided and apt to derail, and, in turn, apt to be blocked under the detection car, which influences severely the running safety.
Therefore, an object of the invention is to provide an ultrasonic flaw detection method for detecting rail flaws using wheel transducers, as well as the wheel transducer and the flaw detection system for implementing the method, so that the echo signals are received correctly even in high speed flaw detection, with the missing echo signals significantly reduced, the interfering waves lowered, and the running safety considerably improved.
According to a first aspect of the invention, an ultrasonic flaw detection method for detecting rail flaws using wheel transducers is provided, comprising the following steps: generating continuous ultrasonic pulse beams; coupling the beams through coupling medium into the rail to be detected; detecting the echo signals of the beams reflected from the rail and processing said echo signals to determine whether there is any flaw in the rail. The method is characterized in that the coupling medium used in the coupling step is solid.
According to a second aspect of the invention, an ultrasonic wheel transducer for detecting rail flaws for implementing the above method is provided, comprising a tire made of ultrasonic wave permeable materials and probes functioning as ultrasonic emitter/receiver, characterized in that the wheel transducer further comprises a sliding plate and means for reducing friction between the sliding plate and the wall of the tire of the wheel transducer during flaw detection, wherein said sliding plate is fixed on the fixed axle of the wheel transducer, and said probes functioning as ultrasonic emitter/receiver are mounted on the sliding plate, and wherein, in the course of flaw detection, the sliding plate compels the wall of the tire of the wheel transducer to flat press on the surface of the rail to be detected.
Said means for reducing friction may be formed as follows: jetting holes are formed in the sliding plate, and when detecting flaws, coupling fluid of high pressure is jetted out of the jetting holes and forms a thin fluid film between the sliding plate and the wall of the tire of the wheel transducer. Said means for reducing friction may also be comprised of rollers or balls mounted on the sliding plate, said rollers or balls being pressed against the wall of the tire of the wheel transducer. The means for reducing friction may still also be as such: necessary small gap is maintained constantly between the sliding plate and the wall of the tire of the wheel transducer by means of automatic control techniques, so that the wheel transducer rolls smoothly on the rail.
According to a third aspect of the invention, it is provided a wheel-type ultrasonic flaw detection system for detecting rail flaws for implementing said method, comprising fixing means for mounting the system on the body of detection car and elevating means associated with the fixing means, characterized in that, the system further comprises wheel transducers mounted on the elevating means through a fixing base, said wheel transducer comprises a tire made of ultrasonic sound wave permeable materials, probes functioning as ultrasonic emitter/receiver, a sliding plate and means for reducing friction between the sliding plate and the wall of the tire of the wheel transducer in course of flaw detection, wherein the sliding plate is fixed on the fixed axle of the wheel transducer, the probes functioning as ultrasonic emitter/receiver are mounted on the sliding plate, and, in course of flaw detection, the sliding plate compels the wall of the tire of the wheel transducer to flat press on the surface of the rail to be detected.
According to the above solutions, the ultrasonic wave beam directly passes through the solid sliding plate into the rail, so that the delay of the ultrasonic wave occurring when using coupling fluid is considerably reduced, and the echo signals are received correctly even in high speed detection. Additionally, since the coupling surface necessary for detecting is formed by the wheel transducer""s tire which is compelled by the sliding plate to flat press on the surface of the rail to be detected, the coupling surface can be kept planar even in high speed detection, so that the opportunities of missing echo signals and appearing interfering waves are eliminated, at least reduced. Moreover, according to the invention, the detecting support is no longer necessary and running safety is improved significantly.